1. Field of the Invention
This invention relates to a switched mode regulated DC to DC converter for maintaining a predetermined supply voltage in response to a varying DC power source and circuit loads.
2. History of the Prior Art
Regulated DC to DC converters achieve their objective of delivering a predetermined DC voltage in response to a changing DC voltage source and loads by various approaches. Some first route an AC input voltage through a transformer to obtain an AC voltage close to the desired DC voltage. Next, that AC voltage is rectified and filtered so the resulting DC voltage can be processed through circuitry for maintaining the desired supply voltage. An alternative is to first rectify and filter the AC input voltage and feed the large value of DC voltage through the circuitry designed to obtain the required supply voltage.
Once a DC supply voltage is obtained, simple voltage regulators will feed this DC voltage to a power transistor to furnish the current to the driven load. Regulation of the load voltage occurs by comparing the voltage delivered to the load with the reference voltage. As the DC supply levels vary due to fluctuations in the available AC source and the load requirements, the transistor will receive compensating voltage levels to maintain a constant value of load voltage. Consequently, when the DC supply varies to increase the load voltage, the comparator circuit will decrease the voltage to the power transistor to decrease the voltage delivered to the load to the regulated voltage value. Likewise, decreases in DC supply levels, when sensed, increase voltage values sent to the transistor which cause the supply to deliver more current to the load to maintain the regulated voltage.
The problem with the described regulator is its poor efficiency. The DC voltage source or the control circuitry must necessarily be greater than the output or load voltage since fluctuations in the AC supply as well as the current demands of varying loads must be accommodated. Also, the circuitry in prior systems used their power transistors in the linear range of operation rather than at the saturation points. Consequently, the power lost at the transistor was equal to the voltage across the partially on transistor multiplied by the current through the device.
The applicant's invention embodies circuitry relating to a switched mode regulated DC to DC converter. By designing circuitry to operate transistors in a completely on and off condition with a minimum of time consumed during switching, wasted power is minimized. In addition, the proper cooperation of the switching circuitry and voltage source elements provides equal durations of voltage during the switching cycle to finish a constant voltage to a load.